accomplished by the use of baffles or packing and is similar in concept to a multitray distillation tower.
Spent-stripped catalyst enters the regenerator where the coke is burned off the
catalyst to restore its activity. The heat generated in the combustion process can
supply all of the needed heat for the process. If excess heat is produced, it can be
removed by external catalyst coolers. The regenerated catalyst flows back to the
base of the riser where the cycle is completed. Typical catalytic cracking units
undergo 100–400 of such cycles a day.
Table 3 Deep catalytic
cracking (DCC) versus
FCCU
Process
FCC
DCC type 1
DCC type 2
Yields, wt%
Dry gas
3.5
11.9
4.0
LPG
17.6
42.2
34.5
C5 + gasoline
55.1
27.2
41.6
LCO
10.2
6.6
9.8
DO
9.3
6.1
5.8
Coke
4.3
6.0
4.3
Ethylene
1.1
6.1
1.6
Propylene
4.9
21.0
14.3
Butylenes
8.1
14.3
14.7
Feedstock: Chinese waxy VGO
Product Vapors
Riser Termination Device
Reactor
Stripper
Steam Rings
Spent Cat. Standpipe
Recycle Nozzles
Feed Nozzles
Reactor Riser
Withdrawal Well
Reactor
Single Stage Cyclones
Regenerator
Regenerator
Two Stage Cyclones
Regenerator
Air Distributor
Air Ring
Regen Cat. Standpipe
Slide Valve
Fig. 3 Reactor-regenerator of a modern FCCU
266
W. Letzsch